1. Field of the Invention:
The present invention relates to unsaturated polyester resin compositions containing monomeric styrene wherein the volatilization of the styrene ingredient is suppressed by additives including hydrocarbon wax.
2. Description of the Prior Art:
Unsaturated polyester resin compositions normally include monomeric styrene as a copolymerizable monomer. The solution of monomeric styrene and unsaturated polyester resin is frequently identified as polyester resin syrups. The styrene customarily is present in an amount from 20 to 55 weight percent of the syrup. When polyester resin syrups are employed in hand lay-up or spray-up applications to produce glass fiber reinforced plastic products, the styrene monomer has a tendency to volatilize. The styrene volatilization is objectionable because
(a) the cost of the lost styrene is appreciable; PA0 (b) the variable loss of styrene from day-to-day and batch-to-batch may result in non-uniform product performance; PA0 (c) the presence of styrene vapors in the atmosphere at the workplace constitutes a hazard to plastics workers. PA0 alpha, beta-ethylenically unsaturated dicarboxylic acid; PA0 glycol; and PA0 linseed oil fatty acids. PA0 alpha, beta-ethylenically unsaturated dicarboxylic acid or anhydride; PA0 glycol; and PA0 linseed oil fatty acids.
Because of the workplace hazard, certain threshold concentration limits for styrene vapors have been established. In order to satisfy these limitations, it has been customary to introduce small quantities of hydrocarbon wax into the composition. The hydrocarbon wax tends to migrate to the surface of the plastic part during its formulation and to serve as a film which confines the styrene monomer within the part. While such systems have successfully suppressed the styrene volatilization, the products are deficient in secondary bonding characteristics. Customarily in hand lay-up and spray-up applications, relatively thick glass fiber reinforced plastic articles are produced in several layers. A first layer is applied and allowed to cure; thereafter a second layer is applied over the first layer and allowed to cure; thereafter, in some cases, additional layers are applied over the preceding layer and allowed to cure. The multiple layers are employed particularly with reinforced plastic products which have appreciable thicknesses. It is necessary that each succeeding layer achieves an acceptable bond to the preceding layer. Such bond is identified as a sedondary bond. In order to avoid the recognized shortcomings of the secondary bonding with styrene suppressed resins containing hydrocarbon wax, it has been recommended that each layer of the product be sanded or wiped with solvent or both before application of a second or succeeding layer of polymerizable plastic, particularly if the second or succeeding layers are to be applied more than 24 hours after the preceding has been applied.
There exists a need in the art to provide a polymerizable unsaturated polyester resin composition including monomeric styrene in which the volatilization of the styrene is successfully suppressed to acceptable levels without adversely affecting the secondary bonding characteristics of the resulting products.